A joint team of international researchers has unveiled its latest achievement: a 3D printing method that allows printed objects to permanently transform into different forms when exposed to heat. The new technique, a type of 4D printing, was the result of research conducted by the Georgia Institute of Technology in the U.S., the Singapore University of Technology and Design (SUTD), and the Xi'an Jiaotong University in China.

4D printing, which introduces the element of time and movement into 3D printing, has been in development for some time, with researchers from around the globe developing various different printable materials that can change form once exposed to elements such as water and heat. Much of the existing 4D printing research has relied on the use of hydrogels, which are incredibly soft, making it difficult for them to maintain their form once they have transformed.

With new research coming out of Georgia Tech, SUTD, and Xi'an Jiaotong, however, it now seems to be possible to create 3D printed objects that can transform permanently, marking a significant step forward for 4D printing technology. The research was recently published in the journal Science Advances under the title "Direct 4D printing via active composite materials.”

The 4D printing process consists of 3D printing layers of shape memory polymers (SMPs), with each layer essentially programmed to react differently when exposed to heat. SMPs, for those unfamiliar, are smart polymers which are designed to “remember” their original shape and to shape-shift into a pre-determined shape when heat is applied. A previous study by the research team dealing with SMPs was able to make objects that could fold on themselves using hinges.

Jerri Qi, a professor from the George W. Woodruff School of Mechanical Engineering at Georgia Tech, said of the new method: “This new approach significantly simplifies and increases the potential of 4D printing by incorporating the mechanical programming post-processing step directly into the 3D printing process. This allows high-resolution 3D printed components to be designed by computer simulation, 3D printed, and then directly and rapidly transformed into new permanent configurations by simply heating.”

To demonstrate the new 3D printing technique, the research team manufactured a number of different transformable objects, including a rather complex flower whose petals contract and bend when exposed to hot water, and a lattice structure which can expand up to almost eight times its original size when placed in the same water.

"Our composite materials at room temperature have one material that is soft but can be programmed to contain internal stress, while the other material is stiff," explained Zhen Ding, a postdoc researcher at SUTD. "We use computational simulations to design composite components where the stiff material has a shape and size that prevents the release of the programmed internal stress from the soft material after 3D printing. Upon heating the stiff material softens and allows the soft material to release its stress and this results in a change—often dramatic—in the product shape."

As seen in the demo videos, the transformations for the 3D printed objects is remarkably fast, taking only about five seconds to complete—much faster than previous hydrogel 4D printing techniques. The researchers even have some degree of control over the final transformed shape, as it is controlled via various printing parameters which are implemented.

While the process is still in its early stages, the technology does show promise for a number of different applications. For instance, 4D printed objects could be extremely useful for creating compactly stacked or rolled structures, which can be shipped easily and then expanded when they are needed. The research team even says that it could one day be possible to have objects react to different types of stimuli, such as light, or even electricity.

Martin L. Dunn, a professor at SUTD, said the technique "promises to enable myriad applications across biomedical devices, 3D electronics, and consumer products," adding that it "even opens the door to a new paradigm in product design, where components are designed from the onset to inhabit multiple configurations during service.”